rc ledger: don't use region highlighter for simple keywords

As reported in
https://github.com/mawww/kakoune/issues/4685#issuecomment-1200530001
ledger.kak defines a region end that matches every character of
the buffer. This causes performance issues for large buffers.
Since the affected regions are only ever filled with a single color,
just use a regex highlighter instead of a region highlighter.
This improves performance when loading the file for the first time.

Speedup on [example.journal.txt](https://github.com/mawww/kakoune/issues/4685#issuecomment-1193243588)

	$ HOME=$PWD hyperfine -w 1 'git checkout HEAD'{~,}' -- :/rc/filetype/ledger.kak && ./kak.opt example.journal.txt -e "modeline-parse; hook global NormalIdle .* quit" -ui dummy'
	Benchmark 1: git checkout HEAD~ -- :/rc/filetype/ledger.kak && ./kak.opt example.journal.txt -e "modeline-parse; hook global NormalIdle .* quit" -ui dummy
	  Time (mean ± σ):     362.1 ms ±   5.1 ms    [User: 336.6 ms, System: 30.2 ms]
	  Range (min … max):   352.6 ms … 369.1 ms    10 runs
	 
	Benchmark 2: git checkout HEAD -- :/rc/filetype/ledger.kak && ./kak.opt example.journal.txt -e "modeline-parse; hook global NormalIdle .* quit" -ui dummy
	  Time (mean ± σ):     271.2 ms ±  16.7 ms    [User: 252.8 ms, System: 24.0 ms]
	  Range (min … max):   253.9 ms … 305.0 ms    10 runs
	 
	Summary
	  'git checkout HEAD -- :/rc/filetype/ledger.kak && ./kak.opt example.journal.txt -e "modeline-parse; hook global NormalIdle .* quit" -ui dummy' ran
	    1.33 ± 0.08 times faster than 'git checkout HEAD~ -- :/rc/filetype/ledger.kak && ./kak.opt example.journal.txt -e "modeline-parse; hook global NormalIdle .* quit" -ui dummy'

0 files changed, 0 insertions, 0 deletions